The invention relates to a coupling element of a mufti-joint crank drive of an internal combustion engine, including a coupling lever and a bearing cover, wherein the coupling lever surrounds a first eye for a piston connecting rod of the crank drive, a second eye for an articulation connecting rod of the crank drive and together with the bearing cover a third eye for a crank pin of a crankshaft, wherein the coupling lever and the bearing cover abut one another on the outer periphery of the third eye in a separating plane passing through the center of the third eye and are bolted to each other by two bolts, and wherein the two bolts have parallel longitudinal central axes. The invention further relates to a multi-joint crank drive of an internal combustion engine with a plurality of such coupling elements.
Coupling elements of the type mentioned above are used in multi-joint crank drives of internal combustion engines as connecting members between the piston connecting rods connected to the pistons, the corresponding crank pins of the crankshaft, and associated articulation connecting rods connected to an eccentric shaft. The working stroke of the piston of the internal combustion engine can be adjusted by means of the multi-joint crank drive so that different working strokes of the piston result in different working cycles of the internal combustion engine. The working stroke is hereby understood to be the distance which lies between an upper and a lower dead point of the piston, i.e. the maximum distance traveled by the piston during the working stroke. Alternatively or additionally, the compression ratio can be set by the multi-joint crank drive, which is realized in the cylinder associated to the piston, in particular depending on the operating point of the internal combustion engine and/or the working stroke of the cylinder.
A coupling element and a multi-joint crank drive are already known from DE 10 2011 116 609 A1 of the applicant. The known coupling element has a split third eye and includes a coupling lever and a bearing cover connected to the coupling lever by two bolts, each forming one half of the third eye. The coupling lever and the bearing cover abut each other on the outer circumference of the third eye along two lines of contact, which span a separating plane passing through the center of the split third eye. In order to provide high strength with low mass, the coupling lever and the bearing cover are connected together by two bolts defining longitudinal central axes which are not parallel to each other but are aligned “skew”.
The publications EP 1 247 960 A2, EP 1 914 405 A2, and JP 2004-124775 A are also known in the art.
It has been shown that multi-joint crank drives with coupling elements, in which the coupling lever and the bearing cover are connected to one another by such “skewed” bolts, cannot be realized on a large scale with the necessary bolt tightening and monitoring procedures.
Therefore, solutions are sought with which a high strength can be achieved for coupling elements whose bolts have parallel longitudinal central axes, despite low coupling element mass. This poses difficulties especially when the distance between the third eye and the first eye should be kept as small as possible and therefore the screw hole for the bolt arranged on the side of the first eye shall no longer pass through between the first and third eyes as in the coupling element from DE 10 2011 116 609 A1.